You'll still get a better challenge with the original STW v1.12 campaign. The reason being that the AI clans can build infrastructure and train units at the maximum rate while you, the player, have to divide your resources between building and training. I started an STW v1.12 Takeda campaign (normal difficulty) last night, and within 6 years the choice between infrastructure and training has already become problematic. I desperately need Takeda Shingen to come of age so that I can engage the AI clans and reduce the size of their armies and take away some of their infrastructure. As I recall, you have to win battles consistently inflicting at least a 2:1 casualty ratio to keep pace. You can't sit back and not attack. You have to risk counterattack by a neutral clan. Making allies reduces a clan's inclination to attack you, so this is an important consideration.
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